Resonator structure



June 5, 1956 u wrrsc EI'AL 2,749,438

RESONATOR STRUCTURE Filed Aug. 21, 1952 3 Sheets-Sheet l Inventors:

Anatole M.Gur-ewitsch,

Philip C. Noble,

27 by )Q/d W Th eir- Attorney.

June 5. 1956 A. M. GUREWITSCH ETAL 2,749,438

RESONATOR STRUCTURE Filed Aug. 21, 1952 3 Sheets-Sheet 2 Fig.5.

Inventors: Anatole M. Gurewitsch, i Philip C. Noble,

by 7 4. Their- Attorney.

United States Patent RESGNATQR STRUGTURE Anatole M. ,GurewitschandPhilip :C. Noble, Schenectady,

N. Y., assignors to GeneralElectr-ic Company, a corporation ,of New YorkThe present invention relates to; high frequency resonators and, moreparticularly, to resonatorsfindin'g useful application in apparatusfor-imparting hig'h energy tocharged particles. i

The invention is applicable in connection with appae ratus of the typedisclosed in United States Patent No. 2,485,409, patented October 18,1949 by Herbert C. Pollock and Willem F. Westendorp, and assigned to theassignee of the present invention. Such apparatus comprises means forinitially accelerating charged particleswithin an evacuated annularenvelope by the action of a field, produced by a time-varying magneticflux, and for thereafter imparting additional energy to the particles bya' localized electric field'of cyclically-vary ing character.

In one-form of this charged particle acceleratingap paratus, the meansemployed for producing the localized.

electric fields comprises a space resonant structureor resonatorsuitably located along the path of the charged particles within theregion of the time-varying magnetic flux. To facilitate the assembly ofa vacuum-tight en velope enclosing the particle path and the desiredclose coupling-of the electric fields'with the path of the chargedparticles, the space resonant structure or resonator is formed'as asector of the annular envelope which itself is divided into sectors ofequal length. Sincethe physical-length of theresonator is thusdetermined, it'very often occurs that the resonant frequency oftheresonator does not correspond to that required for the successfulacceleration'of charged particles withinthe apparatus.

Accordingly, it is a principal object of the present-invention'toprovide a novel space resonant structure-or resonatorin which theresonant frequencymay be'varied without. altering the physical. lengththereof.

It is another object of the invention to provideanovel space resonantstructure or resonator which is adapted for employment with chargedparticle accelerator apparatus and which may be tuned without anyalteration inits physical length.

It is still another object of the invention to provide novel means fortuning a resonator without altering its physical length and withoutdisturbing theelectrical symmetry of the structure.

It is-yet another object of the invention to provide novel means fortuning a resonator without deleteriously affecting the shielding of theelectromagnetic oscillations produced therewithin.

Inaccordance with one aspect of the invention more fully-describedhereinafter, there is provided a resonator formed of a tubular sectionof dielectric material .upon the outer and inner surfaces of which aresupported layers of conductive material. 'These layers respectivelyconstitute the inner and outer conductors of the resonaton; By-theprovision of ca noneconductive gap around the inner periphery of thetubular section, high-frequency lectric-fields are caused to appearwithinthe inner @011: ductorpf the resonator when it is, excited"with-high free que sy ene g In o 0 enable un of ilk- 9 9 2,749,438Eatented June 5, 1956 tor,- .the outer conductor is made discontinuousalong. at least a portion of the periphery of the tubular section,andx'aninductive member including a layer of conductive material isconnected across the discontinuous portion. The inductive member isarranged to. have a desired length longer than the discontinuous portionof the outer conductor whereby the resonant frequency of the resona, tormay be varied Without changing its physical length;

Thefeatures of the invention desired to be protected herein are pointedout with particularity in the appended claims; The invention itself,together with further ob.- jectsand advantages thereof, may best beunderstood by reference to lheifOllOW'lrlg description, taken in con!nection .withthe accompanying drawings, in which Fig. l isapartially'sectionalized elevation .ofan accelerator suitablyembodying theinvention; Fig. 2 is'a'plan' view' of the annular envelope or dischargevessel shown in Fig; 1; Fig. 3 isasectionview taken along lines -33ofFig. 2; Fig. 4 isan enlarged perspective view of the resonatorstructure :ofiFig: 2; Fig. 5 is a partially sectionalized view of:apreferred arrangement for exciting. the resonator structure of theinvention; Fig. 6 is a fragmentary sectionalized view of alternativeresonator structure according to the invention; Fig. 7 is a fragmentarysectionalized view. of another alternative embodiment of resonatorstructure according to the invention; and Fig. 8 is a schematicrepresentation of excitation apparatus -employed in connection. with thedevice of Fig- 1.

Referring particularly to Fig- 1, there is shownin section. a closedrotationally symmetrical envelope ll) which. defines withinits interioran annular chamber. Theenvelope. 10, which is preferably constructed. ofglass. or ceramic material, provides a circular orbit-in which chargedparticles, e. g., electrons derived from a suitablyenergized source 11supported from a side arm 12, .may be'acceleratcd to a high energylevel. The envelope 10 is preferably highly evacuated and 'isprovided onitsinterior surface with a high resistivity, conductivecoating (notshown), .forexample, a layer of a metallic salt, in order to reduce theeffect of wall charging, Forming a sector of envelope 10 is a resonatorstructure which does not appearin Fig. .1, but which will be shown. anddescribed-at a later point.

Theenvelope or vessel ,1!) lies symmetrically around the axis of alaminated magnetic structure having acen! tral flux, path provided by anannular iron core 13. This .core is supported at its. extremities byattachment to the central portions of opposed pole pieces 14 and 15which. have planar circular areas 16 and 17 and tapered annular areas 18and 19. The pole pieces 14 and .15. are, in turn,. supported by arectangular-frame 20:.oflaminated iron which surrounds-and extendstransversely to the envelope 10.

Ihe ,endsfof the core 13 are separated from thepole pieces 14 and 15 .bynarrow gaps 21 and 22 which are so proportioned .as to cause the core tosaturate at a predetermined level of the magnetic flux passing throughit. Preferably gaps 21 and 22 are filled by washers of nonmagneticmaterial (not shown) for the purpose of assistnelfin the proper supportof core 11. Theiannular faces 18 and 19 of the two pole pieces each havea double taper aswshown, the purpose of this configurationbeingexplained ata later point. An opening 23, which extendsicontinuouslyihrough the frame 20,. pole pieces 14 and 15, andcore .13,permits .cooling air to be circulated through theseparts.

The'magnetic structure is excited by means of a pair gfseries connectedcoils 25 and 26 which. surround the polepieces and. which may beenergized'in .such .a manner jas tof provide a time or.cyclically-varying-flux in the magnetic.circuit. Electrons producedwithin the envelope 10 .are affected in two ways by the variations inmagnetic flux thus obtained. In the first place, since the magnetic fluxtraversing core 13 links the circular path provided by envelope 10, anyvariation of such flux necessarily produces an electric field tending toaccelerate electrons projected along such paths. In this latter respect,the apparatus is comparable to a transformer with a secondary comprisinga circular path along which the various electrons are accelerated.

In general, although the voltage per turn in such a transformer may below, within a practically attainable range of flux variation, theelectrons can be made to achieve very high energies, e. g., severalmillion electron volts, because of the tremendous number of turns whichthey may execute during a single cycle of the magnetic flux variation.In addition to the acceleration produced by the time-varying magneticflux linking the electron path, the flux produced by the annular polepieces 18 and 19 in the region of the electron orbit tends to cause theelectrons to follow an inwardly spiraling path. It has been shown thatwith a proper design of the magnetic structure, the centripetal forceproduced by the magnetic field existing at the electron orbit may becaused to'balance the centrifugal tendencies of the acceleratedelectrons. In general, this result requires that the followingrelationship be satisfied:

where 6 is the flux included in the electron orbit, r is the radius ofthe orbit, and Br is the field strength at the orbit. This equationindicates that the flux incuded in or linking the orbit must be twice asstrong as that which would be produced by a homogeneous field equal tothe field Br extending over the entire area enclosed by the orbitalelectron path. This conditon may be realized by making the reluctanceper unit of cross-sectional area of the magnetic path at the electronorbit greater by an appropriate amount than its average reluctanceWithin the orbit. In order to maintain the desired proportionalitybetween the enclosed fiux and the guide field, i. e., the field Br atall times during an accelerating period, one may adjust the air gapexisting between pole pieces 18 and 19 to the appropriate value. It isreadily practicable to control the dimensions of the gap from point topoint over the pole piece in such a fashion as to effect the balancedrelation of guide field and enclosed flux which is desired for thepurpose specified above and which is further necessary for radial andaxial stability of the electron orbit. This may be done, for example, bya construction such as that shown in Fig. l in which the pole pieces aredoubly tapered. The principles governing the proper space distributionof the guide field are more fully set forth in United States Patent2,394,070, granted February 5, 1946, to D. W. Kerst.

When all the conditions specified in the foregoing are fulfilled,electrons introduced into envelope in a period when the magnetic fieldis increasing may be expected to be drawn into the particular orbit inwhich a balance of centripetal and centrifugal forces exists and to becontinuously accelerated along such orbit as long as the magnetic fieldincreases in value. Assuming that the peak value of the magnetic fieldis sufficiently high, a total energy on the order of several millionelectron volts may be acquired by the accelerated electrons in a smallfraction of a second.

It may be noted, however, that when an electron has obtained a velocitycorresponding to an energy level of about three million electron volts,it is already within about 1 percent of the velocity of light.Accordingly, further gains in energy result primarily in an increase inthe mass of the affected electrons and only insignificantly in furthergain in electron velocity, this result being consistent with theEinstein mass-energy equivalence formula. Therefore, electrons whichhave attained a velocity within a few percent of the velocity of lightwill gyrate with a relatively constant periodicity, or at a relativelyfixed where c is the velocity of light, r is the radius of thefrequency, provided they can be confined to an orbit of relatively fixedradius. As is pointed out in the aforementioned United States Patent No.2,485,409 of Pollock and Westendorp, this consideration makes itpossible to impart further energy to the electrons by means of alocalized electric field of fixed frequency acting repetitively on theelectrons as they continue their gyrations within the envelope 10. Bythis means, extremely high energy levels can be reached through amechanism which avoids difficulties associated with any attempt toachieve corresponding energy levels by a magnetic acceleration alone.With this in mind, the apparatus of Fig. l is so constructed thatsaturation of core 13 occurs after a sufficient acceleration of theelectrons has been obtained by magnetic means, and an electric fieldaccelerating device to be hereinafter described is brought into play. Inorder that the accelerated electrons may still be confined to thedesired orbit, however, the guide field produced between pole pieces 18and 19 continues to increase as a result of continued energization ofcoils 25 and 26.

As is illustrated in Fig. 2, envelope 10 is formed of a plurality ofsectors 27 of dielectric material which may be joined together invacuum-tight relation by means of suitable rubber gaskets (not shown) ina manner well known to those skilled in the art. T o assure themaintenance of an evacuable space within envelope 10, the surfaces ofjuncture of the rubber gasket and the envelope may be coated with adesired adhesive material, for example, an alkyd resin prepared byreacting a polybasic acid and a polyhydric alcohol, such as a resinbeing prepared from glycerol and phthalic anhydride. Alternatively, therubber gaskets may be omitted and the abutting surfaces of sectors 27coated with the adhesive material. The ease with which envelope 10 maybe constructed is assisted by making each of the glass or ceramicsectors 27 of equal lengths, inasmuch as this permits the manufacture ofthe sectors such that closely matched end surfaces are obtained withoutan excessive expenditure of effort. Formed as a sector of envelope 10 isa space resonant structure or resonator 28 which will be more fullydescribed later.

In connection with the description of the apparatus of Fig. 1, it hasbeen stated that the electrons introduced into envelope 10 are firstaccelerated to within about 1 percent of the velocity of light by atime-varying magnetic flux, and then are further raised in energy levelby means of a localized electric field of fixed frequency actingrepetitively on the electrons as they continue their gyration within theenvelope 10. In order to obtain repetitive acceleration of theelectrons, the frequency of the localized electric field must satisfythe following relation:

orbit, and f is the frequency. It is apparent from Equation 2 that, oncea desired orbital radius is selected, the frequency of the localizedelectric field is immediately determined. It will be observed, however,that resonator 28, which supplies the localized electric field accordingto the invention and which comprises inner and outer conductorssupported upon a tubular section of dielectric material, has a resonantfrequency which is a function of. the length of the resonator and thedielectric constant e of the material employed. Its resonant frequencyis given by where h is the resonant frequency and L is the centralarcuate length of the structure. Therefore, as may be seen from Equation3, for a given dielectric material, the resonant frequency f1 ofresonator 28 is determined by its length L which, in turn, is fixed bythe above= 3 mentioned ..construction of envelope zfrom,,sec t ors,ofequal: length. Accordingly, if the resonant, frequency, ft of resonator.28 does not correspond to thefrequency f required.:by.Equation 2,further energy cannot .besuccessfully imparted to the electrons by thelocalizedelectric field. within resonator 28.

The present. invention supplies anadvantageous and efiicient solution tothis problem bytheprovision, of the novel resonator 28, the frequency ofwhich may be varied without altering its physical length. As is moreclearly shown in Figs. 3 and 4, space resonant structure or resonator 28forms a sector of envelope 10 and comprises agtubular section 29ofdielectric. material-having an approximately elliptical cross sectionwhichconfo'rms, to the cross ,sectionof envelope 10. Since it ispreferable to; utilize a dielectric material having a smallhighfrequency loss coefficient, tubular section 29 may be formedof amaterial such as .fused quartz or ceramic and shaped similarly tothesectors 27 of. envelope .10. In order to provide means for conductinghigh frequency currents, tubular section 29is coated upon all itsexposed surfaces with a layer 30 of conductive'material, such as silver.Portions 31 ofcoating 30 are removed. from the exterior surfaceofsection 29 toforma plurality .of approximately evenly spacedconductive strips 32 extending longitudinally along both sides thereof-Portions 31 are discontinuous adjacent one end of section 29 in order toprovide aperipheral conductiverstrip33. In alike manner, portions 34 areremoved from coating30 on the inner. surface of section ,29to form aplurality of conductive strips 35; extending longitudinally. therealong.Portions 34 are discontinuous to provide peripheral conductivestrips 36and 37. A peripheral gap 38 is provided byremovinga portion-betweenstrips 36:and 37. Portions 39aareremovedfrom the end surfacestone ofwhich is not shown) .of section 29 to produce a plurality ofconducti-ve. strips 40; Portions 31, 39 and 34, removed respectivelyfrom the coating upon the exterior surface, end faces, andinnersurfaceof section 29, are spatially interrelated sothat .each,strip 32' is conductively-connected to the oppositely disposedstripy35ruponthe adjacent inner surface of section29.

One convenient way of formingconductive layer 30 is as follows. A layerof silver paint. is placed upon the inner surface,..outer surface andendfaces ofrse ction 29 and subsequently baked to secure adherencethereto. The thickness of this layer may beincreascd by means ofelectroplating,.,or by repeated painting and baking, for the purpose ofobtaining a layer havinga thickness greater than the depth ofpenetration of the high frequency current which flows therein whenresonator 28 is excited. As an order of magnitude, the layer may have afinal thickness of about 1 to 1 /2 mils when the resonator is to beexcited at 160 me. The various portions removedifrom the conductivelayer as above describedmay be made by masking'during th'e paintingoperation-, or-by burning-in grooves, after the painting andelectroplating, with a tungsten disc which is rolled along theconductive-surface carrying a heavy current through the contact area;

As is disclosed in United States Patent-No. 2,579,315, patented December18,:1951, and assigned to the assignee ofthe present invention, thesubdividing -of coating 30 into longitudinal strips provides aconvenientand direct means. of reducing eddy currents induced: inresonator 28rbyithe time-varying magnetic flux which traverses thestmcturetwhen.theaccelerator apparatus'of the invention isrin operation.With, the particular interconnection .of the. longitudinal; strips byperipheral conductive strips .33, 3.6-;and :37 in :the.mannerillustrated, nearly complete compensation ofinducededdy currents may be;obtained whereby undesirable heating of the stripszis avoided; Moreover,this interconnection of the strips increases the coupling therebetweenand. prevents the oscillationv of resonator 28 ,in undesirable ,modes.It, will, ,be observed that .theJQngitudinal subdivision 20fcoating-.30: need .not

becontinned adjacent. the innerand outer circumference of, resonator -23=inasmuch as. .-such.,.por.tions are nearly parallel to the :directionof the time-.varying-fiux andtherefore ,will not have appreciable'eddycurrents induced therein.

With the :longitudinal dimensions determined in the above-describedmanner by the construction of the, envelope 10 from sectors of equallength, resonator-28 operates as aquarter-wave, closed concentric lineresonator at a particular excitation frequency. The space between theconductive coating on the exterior surface of section 29 and the coating.on the interior surface ,con: stitutes in effect a space resonantsystem comprisinga quarter-wave transmission line section. Accordingly,if resonator. 28 is excited at its resonantfrequency, a cyclicallyreversible electric field of. high intensityappears across gap 38. Ifthe resonant frequency of resonator v28 as expressedby Equation 3corresponds "to the frequency of rotation of electrons moving withinenvelope 10 and section 29-as expressed by Equation 2,. an in crease inthe energy level of such electrons may beeffected in accordance withtheprinciples previously outlined.v

Since the physical length of resonator 28 as determined by theconstructional requirements of envelope 10 very seldom provides aresonant frequency which corresponds to the frequency-of rotation ofelectrons within envelope 10,- the present invention contemplates meansfor tuning or varying the resonant frequency of resona? tor ,28 withoutaltering its physical length. In general, itisfeasible to increase theresonantfrequency of resona tor 28 by moving gap 38 along section 29away from the end which it is adjacent. However, when it is :necessaryto lower the resonant frequency of resonator 28, severe difficultiesarise because-gap 38 obviously cannot be moved beyond the end ofsectionv29 whichit is adjacent. According to the present invention,therefore, there ;is provided an inductive member 41 which'is PQSi?tioned adjacent the end of section 29 remote from gap 38;Inductivemember 41 comprises an-annular band 42 of dielectric materialsupported upon section 29 about theexterior surfaces of strips=32.-Extending along vthe exposed sufaces of band 42 is a layer ofconductivemate, rial. 43 which is ubdivided into strips 44 corresponding inperipheral position to conductive strips 32. Ifconductive coating 43-andstrips44 are formed upon band 42 separate from the formation ofconductive coating lid-and strips32 upon section 29, conductiveconnection therebetween may be assured by soldering the adjoiningsurfaces. Conductive coating 30 and strips 32 are made discontinuous toforma peripheral gap 45 wherebyconductive coating 43 and strips 44constitute in effect ;a longitudinal extension of conductive coating 30andstrips 32. Thus, conductive layer 43 and strips 44, which areconnected across gap 45, add inductance togresonator 2S and lower itsresonant frequency without requiring any alteration in the physicallength of resonator;28.-.

it will be observed that inductivemember 41 is-posi'- tioned adjacentthe end of resonator 2-3 where the high frequencycurrents are large andthe electricfields Within the dielectric are small. Therefore, thechoice of dielectric material required for band 42 isnot critical.Conveniently, it may consist of an organic material such aspolystyrene.Alternatively, band 42 may be constructed by impregnating strips ofglass cloth With.a solventless varnish such as a resinsynthesizedfromtiiethylene glycol 'maleate and diallyl phthalate, distributing theimpregnated glass cloth within a suitable -rnold, and curing inaccordance with principles Well known-to those skilled. in the art. Ifthe dielectric material selected .for band-42 is not capable ofwithstanding the :heat: necessary for the application of a conductivecoatingof silver in the manner heretoforedescribed, conductive..coating.43 and strips 44 may be formed of thin, conductive materialsuch ascopper secured to the surface -0fjb3l'3d 42.by means otasuitableadhesive, e. g., the aboveamena tioned alkyd resin. If desired,conductive layer and strips 32 may likewise be formed of thin conductivematerial secured to the surfaces of section 29.

In Fig. 5, wherein like reference characters are employed to designateelements hereinbefore presented, there is illustrated a suitable meansfor exciting resonator 28 with high frequency energy. A portion 46 isremoved adjacent the outer circumference of section 29 to provide alongitudinally extending conductive strip 47. Although strip 47 is shownas being joined at its lefthand extremity to the remainder of layer 30,it may in some cases be made entirely separate therefrom by extendingportion 46. Energy may be supplied to resonator 28 by the combination ofa conductor 48 which connects with the conductive strip 46 and a tubularelement 49 surrounding the conductor to form with it a concentrictransmission line. At the point where conductor 49 approaches resonator28, it merges into a channel-shaped enlargement 50 which is ofsufiicient longitudinal and lateral extent entirely to cover removedportion 41 and thus to afford high frequency shielding. While conductor48 and the enlarged member 49 are shown as being of metallic crosssection, it will ordinarily be preferable to form them of anon-conducting dielectric internally coated with a thin metal layer inorder to minimize currents induced by the time-varying magnetic field.By choosing the correct dimensions and an appropriate point ofconnection to strip 47, it is possible to accomplish an excellent matchof power from concentric line 48, 49 into the resonator. The length ofstrip 47 may be varied as desired to produce optimum tuning and matchingof the system.

In some installations of the apparatus of Fig. 1, it may be inconvenientbecause of spatial requirements to extend inductive member 41 along theexterior surface of resonator 28 toward the gap 38. In the embodiment ofFig. 6, wherein like numerals are employed to designate similar elementsdescribed hereinbefore, inductive member 41 is shown as extending awayfrom gap 38 over the juncture of the end of resonator 28 and theadjoining sector 27. Layer 43 and strips 44 extend along a substantialportion of the inner and outer surfaces of a flanged annular band 51 ofdielectric material. The flange 52 of annular band 51 may be attached tosection 29 by means of a suitable adhesive, thereby assuring adequatesupport of the inductive member. As will be seen, the construction ofthe inductive member illustrated in Fig. 6 provides a larger addedinductance to resonator 28 for a given circumferential or longitudinalextension of band 51.

In Fig. 7, where like numerals are also utilized to additional supportby the adjacent sector 27.

The operational correlation of the resonator structure and the othervarious elements of the accelerator heretofore considered may best beunderstood by reference to Fig 8 which shows diagrammatically theaccelerating structure as a whole in combination with schematicallyillustrated excitation equipment. In this figure, parts which have beendescribed bear numbers corresponding to those by which they have alreadybeen identified.

Referring particularly now to Fig. 8, there is shown a power source 55adapted to supply excitation voltage of the desired frequency, forexample, cycles, to wind ings 2S and 26 by which the magnetic system ofthe accelerator is energized. A second power source 56 which is assumedto be appropriately connected to source 11 of Fig. 1, and which may bean intermittently energized circuit of the type described in theaforementioned Pollock and Westendorp patent serves to inject electronsinto the envelope 10 at appropriate intervals correlated with thecyclical reversals of the magnetic field. Finally, a high frequencypower source 57 which may consist, for example, of an electronicoscillator, supplies when energized, high frequency potential throughtransmission line conductors 48 and 49, to the inner and outerconductors of a resonator 58 which is identical with one of theresonator structures shown in the preceding figures. Properly correlatedenergization of the magnetic field, the electron injecting means and thehigh frequency power supply for the resonator is accomplished by meansof a timing circuit illustrated schematically by the block 59, it beingindicated that the timing circuit is connected with the various powersupplies by conductors 60, 61 and 62 respectively. Through the action ofthe timing circuit, the system as a whole is controlled in such fashionthat initial acceleration of the injected electrons is accomplished by avariation of the magnetic field up to the point where the electrons haveattained an energy level of several million electron volts. Thereafterby saturation of core 13, the accelerating effect of the magnetic fieldi substantially eliminated and subsequent acceleration of the electronsto high energy levels is accomplished by bringing into operation theresonator 58.

In each of the embodiments, inductive element 41 has been illustrated asextending completely around the periphery of section 29. Thisconstruction is preferred because the electrical symmetry of resonator28 is thereby essentially unaffected. However, in some instances it maybe desirable to extend inductive element 41 around only a portion orportions of section 29 and such is within contemplation of the presentinvention.

While the invention has been described by reference to particularembodiments thereof, it will be understood that numerous changes may bemade by those skilled in the art without actually departing from theinvention. We therefore aim in the appended claims to cover all suchequivalent variations as come within the true spirit and scope of theforegoing disclosure.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. In apparatus for the acceleration of charged particles along a pathwhich is enclosed by an envelope of dielectric material; a resonatorforming a section of the envelope comprising an inner conductor whichincludes a conductive layer supported upon the inner surface of saidsection, and an outer conductor which includes a conductive layersupported upon the outer surface of said section and being discontinuousaround at least a portion of the periphery of said section whichdiscontinuous portion extends in spaced relation around a portion of theinner conductor; and an inductive member for tuning said resonatorincluding a conductive layer connected across the discontinuous portionof said outer conductor, said last-mentioned conductive layer having alength greater than the length of the discontinuous portion of saidouter conductor.

2. In apparatus for the acceleration of charged particles along a pathwhich is enclosed by an envelope of dielectric material; a resonatorforming a section of the envelope comprising an inner conductor whichincludes a conductive layer supported upon the inner surface of saidsection and being discontinuous to provide a non-conductive gapextending around the periphery of said section adjacent one end thereof,and an outer conductor which includes a conductive layer supported uponthe outer surface of said section and being discontinuous around atleast a portion of the periphery of said section which discontinuousportion extends in spaced relation around a portion of the innerconductor adjacent the end remote from said gap; and an inductive memberfor tuning said resonator including a conductive layer connected acrossthe discontinuous portion of said outer conductor, said last-mentionedconductive layer having a length greater than the length of thediscontinuous portion of said outer conductor.

3. In apparatus for the acceleration of charged particles along anorbital path which is enclosed by an annular envelope of dielectricmaterial and traversed by a timevarying magnetic field; a resonatorforming a sector of said annular envelope and comprising an innerconductor including a conductive layer supported upon the inner surfaceof said sector of said envelope and having portions thereof removed toform a plurality of spaced apart conductive strips extendinglongitudinally along said sector, and an outer conductor including aconductive layer supported upon the outer surface of said sector of saidenvelope and having portions thereof removed to form a plurality ofspaced apart conductive strips extending longitudinally along saidsector, said outer conductor being discontinuous around at least aportion of its periphery which discontinuous portion extends in closelyspaced relation around a portion of said inner conductor; and aninductive member for tuning said resonator comprising a conductive layerconnected across the discontinuous portion of said outer conductor, saidlast-mentioned conductive layer having a length greater than the lengthof the discontinuous portion of said outer conductor.

4. In apparatus as in claim 3 in which said last-mentioned conductivelayer is supported upon a band of dielectric material extending aroundat least part of the periphery of said sector, said last-mentioned layerhaving portions thereof removed to form a plurality of conductive stripsextending along said band.

5. In apparatus for the acceleration of charged particles along anorbital path which is enclosed by an annular envelope of dielectricmaterial and traversed by-a timevarying magnetic field; a resonatorforming a sector of said annular envelope and comprising an innerconductor including a conductive layer supported upon the inner surfaceof said sector of said envelope and having portions thereof removed toform a plurality of spaced apart conductive strips extendinglongitudinally along said sector, said conductive layer having adjacentone end a gap extending around the periphery theerof, and an outerconductor including a conductive layer supported upon the outer surfaceof said sector of said envelope and having portions thereof removed toform a plurality of spaced apart conductive strips extendinglongitudinally along said sector, said outer conductor beingdiscontinuous adjacent the end of said sector remote from said gap insaid inner conductive layer to form a gap extending around at least aportion of the periphery of said outer conductor which gap is spaced bysaid envelope from a portion of said inner conductive layer; and aninductive member for tuning said resonator comprising a conductive layerconnected across the gap in said outer conductor, said lastmentionedconductive layer having a length greater than the length of thediscontinuous portion.

6. In apparatus as in claim 5 in which said last-mentioned conductivelayer is supported upon a band of dielectric material extending aroundat least part of the periphery of said sector, said last-mentioned layerhaving portions thereof removed to form a plurality of conductive stripsextending along said band.

7. A resonator comprising an inner conductor which includes a conductivelayer supported upon the inner surface of a tubular section ofdielectric material, an outer conductor which includes a conductivelayer supported upon the outer surface of said section and beingdiscontinuous around at least a portion of the periphery of said sectionwhich discontinuous portion is spaced by said envelope from said innerconductive layer and an inductive member for tuning said resonatorincluding a conductive layer connected across the discontinuous portionof said outer conductor, said last-mentioned conductive layer having alength greater than the length of the discontinuous portion of saidouter conductor.

8. A resonator as in claim 7 in which said last-mentioned conductivelayer is supported upon a band of dielectric material extending aroundat least part of the periphery of said section, and all of saidconductive layers are longitudinally subdivided to form a plurality ofconductive strips extending along said section.

9. A resonator as in claim 8 in which the discontinuous portion of saidouter conductor is adjacent one end of said section and said innerconductor has a peripheral gap adjacent the end of said section remotefrom the discontinuous portion.

10. A resonator as in claim 9 in which said band of dielectric materialand said last-mentioned conductive layer extend beyond said one end ofsaid section.

References Cited in the file of this patent UNITED STATES PATENTS2,304,540 Cassen Dec. 8, 1942 2,434,508 Okress Jan. 13, 1948 2,514,428Varian July 11, 1950 2,553,312 Gurewitsch May 15, 1951 2,579,315Gurewitsch Dec. 18, 1951 2,600,225 Ehrenfried June 10, 1952 FOREIGNPATENTS 976,767 France Nov. 1, 1950 OTHER REFERENCES Meagher andMarkley: Practical Analysis of U. H. F., RCA Service Inc., August 1943,page 7.

